1. Field of the Invention
The present invention relates to an encoder, and more particularly to an encoder which detects a position signal by sliding a slider thereon.
2. Related Background Art
In a camera with a variable focal distance lens, it is necessary to check what focal distance the lens is set to. To this end, a flexible printed circuit board which mounts an encoder having a signal pattern incorporated therein is provided around a cylinder of a lens bodytube, and a slider sliding along a surface of a substrate is used to detect the focal distance.
The encoder used in the prior art has the signal pattern formed by a copper deposition on a surface of a polyester film substrate, and the surface is plated with gold.
A protective pattern (hereinafter called an idle pattern) is provided in order to protect a surface of a polyester film substrate having no signal pattern from abrasion by the slider and to avoid an error signal due to abrasion particles. By properly setting an interval between the idle pattern and the signal pattern, the slider does not contact the surface of the polyester film substrate and no abrasion takes place.
However, because of the need for increased lens information in sophisticated camera systems, the signal pattern of the encoder has become complex. As a result, the idle patterns are also complex and the number thereof increases, and an idle pattern which does not face (is not adjacent to) an outer edge of the polyester film substrate (hereinafter referred to as an island idle pattern) has appeared.
The idle pattern does not necessarily need a lead wire to form the copper deposition, but a lead wire is required on the surface of the substrate in a gold electrolytic plating process.